In a scientific study published on January 11, 2016 in the peer-reviewed journal Food Additives & Contaminants: Part A, Yolanda Echegoyen and colleagues from the Department of Analytical Chemistry, University of Zaragoza, Spain, investigate the migration of nanoclay from two low-density polyethylene (LDPE)-nanocomposite bags.

Polymer nanocomposites consist of an organic polymer and an inert nanoscale filler, the latter added to modify the physical characteristics of the former. Nanopellets of clay (bentonite) in particular are widely used to improve gas barrier properties. In the EU and in Switzerland, some nano-specific provisions are included in the legislation for agricultural products, food and feed. In particular, a nanomaterial has to undergo case-by-case evaluation before placement on the market, even if the equivalent bulk material is already authorized. Currently, only three nanomaterials, namely carbon black, titanium nitride and silicon dioxide, have been authorized for use in plastic food packaging in the EU (see also FPF background article). In many other areas, including the U.S., the regulation for nanomaterials in food contact materials is less specific (FPF reported).

Both products evaluated in this study, Aisaika Everfresh Bag and Debbie Meyer BreadBags, were bought in Japan. Two liquid food simulants (ethanol 10% and acetic acid 3%) and two different contact regimes (40°C for 10 days and 70°C for 2 hours) were assessed. Migration conditions were chosen as to represent the worst-case scenario of prolonged storage and also with the goal to determine if these materials can be used for food packaging in conditions other than stated by the manufacturer. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to measure aluminum in both dissolved and nanoparticle forms, the latter inferred from the presence of spikes during acquisition in single-particle mode. Morphology, size and composition of migrating (nano-)particles were further studied by scanning electron microscopy coupled to energy-dispersive X-ray diffraction (SEM-EDX) technique.

More aluminum migrated from the bag with higher total nanoclay content (Aisaika), but the relative migration was similar for both products. Higher migration was observed with acidic food simulant (by 4-5 times) and for 10 days at 40 °C condition (by 3-6 times), as compared to their respective counterparts. Maximum migration values measured were 51.65 ng/cm2 and 24.14 ng/cm2 for Aisaika and Debbie Meyer bags, respectively. These values are much below the limit imposed by the tolerable weekly intake value of 1 mg aluminum/kg/week, set by the European Food Safety Authority (EFSA) in 2008. However, it has to be noted that this value was established for dissolved species, not for nanoparticles.

ICP-MS showed that most of the migrated aluminum was in soluble form, but aluminum-containing nanoparticles of different sizes were occasionally detected as well. SEM-EDX confirmed the migration of particles with different morphologies and sizes into food simulants. Interestingly, not only clay nanoparticles, but also other micro- and nanosized particles were found. These were composed of carbon and oxygen and hence most likely originated from the polymeric material in the bags (i.e. LDPE).

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